1. Field of the Invention
This invention pertains to a method and apparatus for rearing aquatic animals and, in particular, to a method and apparatus for rearing aquatic animals under controlled conditions.
2. State of the Art
In recent years, attempts have been made to rear aquatic animals under controlled conditions by employing so-called intensive culture systems and methods. U.S. Pat. No. 3,735,736, for example, discloses a method for growing edible aquatic animals, such as shrimp, catfish and trout, on a large scale wherein a series of above-ambient temperature, continuous-flow growing ponds are provided for respectively growing a batch of selected species of aquatic animals to increasingly larger average unit weights. The so-called dwell volume of each pond increases from the smallest where the fry are introduced, to the largest where the adults are recovered. The batch is sequentially transferred from one pond to the next after reaching an average unit weight selected for each pond. The ponds are fed by a stream of water which is at above-ambient temperature by virtue of being derived at least in part from effluent cooling water. The system disclosed is thus an open system since it relies on unlimited resupply of clean water rather than continuous filtration of a relatively fixed water supply.
Further systems and methods more specifically adapted for the rearing of crustaceans from post-larvae size to harvestable adult size have recently received a great deal of attention. A common thread running through many such systems is the provision of habitat structures for the custaceans within the rearing medium. For example, U.S. Pat. No. 3,658,034, issued on Apr. 25, 1972, discloses a system wherein the initial unit of the system comprises a tank provided with a habitat structure formed from a plurality of vertical substrates. Following this initial unit, are a number of further units which include tanks of increasing size and each of which is provided with a habitat structure formed from a number of cylindrical enclosures each for housing an individual crustacean. In this system, the tanks are disposed below one another so the crustacean content of a higher tank can be emptied into a lower tank when the crustaceans in the higher tank have undergone a desired degree of growth. Moreover, in this system, the water in each tank is continuously circulated to remove contaminants therefrom.
Further U.S. Patents which disclose intensive culture systems for post-larvae crustaceans wherein vertically or horizontally aligned substrates are employed as habitats for the crustaceans are as follows: U.S. Pat. No. 3,985,101, issued on July 2, 1975; U.S. Pat. No. 3,916,833, issued on Nov. 4, 1975; and U.S. Pat. No. 3,889,639, issued on June 17, 1975. In the last named patent, the intensive culture system disclosed comprises a plurality of horizontally arranged nets and a filtration system whose filter is backwashed by drainage of some of the water of the system. Moreover, in this system, light is directed through the central area of the nets to attract molting crustaceans to such areas and thereby prevent these crustaceans from being cannibalized by the remaining non-molting crustaceans.